Control system



Jan. 29, 1952 H. E. WURZBACH CONTROL SYSTEM 2 SHEElS- SIEET 1.

Filed Nov. 25, 1945 E I WW2? Mam Jan. 29, 1952 H. E. WURZBACH CONTROLSYSTEM 2 SHEETS-SHEET 2 Filed Nov. 23, 1945 P25. 57. (COMP/148A 711/:PFEFO/PMAAC! 0/42 IN V EN TOR.

1 \Nwk y OW Patented Jan. 29, 1952 UNITED STATES PATENT OFFICE CONTROLSYSTEM Hugh E. Wurzbach, Magna, Utah Application November 23, 1945,Serial No. 630,490

12 Claims.

This invention relates to a control system, and more particularly to onethat is effective to automatically regulate and supervise theperformance of certain machinery, of which a drag-type classifierequipped with rakes is a prominent example. Since this is a typical use,it is convenient to herein described the invention specifically inconnection with such a classifier, in particular a Dorr drag classifier,although the invention is not necessarily restricted to this use.

In classifiers of this type the pulp feed, which consists of more orless finely divided solids sus pended in liquid, such as water, isconducted into a tank having an inclined bottom, The liquid overflowsfrom the tank at a certain level carrying with it the finer solids,while the coarser solids tend to settle on the bottom and are rakedupwardly to be discharged over a ledge located above the liquid level.

Drag classifiers are common in the art of ore dressing and their use ingeneral is well understood. Nevertheless, it is not out of place toquote an authority to the effect that these machines are capable ofadjustment to cover considerable range of conditions and further thatadjustments in slope of classifier tank, rake speed, and dilution ofoverflow pulp are necessary to obtain the desired closeness and mesh ofseparation.

In spie of this assumed capability of adjustment the fact remains thatin actual practice the desired closeness and mesh of separation is notexact, for the reason that the adjustments, such as they are, are moreor less fixed, while the ores, even from. the same mine, vary so greatly in composition that the stated adjustments can be only crudelyapproximated to the average composition of an ore. As a consequence suchad justments still cause a classifier to be overload-ed and choked withthe coarser material at one time, and at another time to be loaded farbelow its capacity with material that is of lesser coarseness.

Among the principal objects of the invention may be summarized thefollowing:

(a) To provide an automatic control system for machines such as Dorrclassifiers, and adapted for running such machines at the minimum speednecessary for best results, consistent with the nature of the materialbeing handled.

(b) To maintain a minimum rake speed for any particular sand load beingmoved, so as to cause the least amount of agitation in the settling areaof a classifier.

(c) To maintain constant, as nearly as pos sible, the level of thecoarse sands just in advance of the discharge ledge.

(d) To maintain the maximum sand load on the rakes regardless of thequantity of feed passing into a classifier; for example, a dragclassifier operates at its maximum efiiciency when the coarse materialis removed as fast as it enters, and settles in, the classifier.

(e) To cause the speed of the classifier to vary in such a, way as toclosely following changing load conditions, since it is desirable tooperate the rakes as slowly as possible, but at the same time to keepthe rakes fully loaded at all times.

(f) To provide periodic supervision.

Further objects will become apparent as the description proceeds. v

In connection with the invention whatever'adjusting means is commonlysupplied as original equipment on the machine concerned to regulatesizes of material discharged and other conditions, must still be used.The device of the invention is intended to serve as a complementthereto. In short, the sole intent of the invention is to bring aboutthe optimum performance of a regularly equipped classifier under any andall changing conditions.

According to the invention it is advantageous to control the speed ofthe classifier rakes rather than the input feed because the input can becontrolled by the maximum capacity of the machinery preceding theclassifier. It is not desirable to regulate the feed entering theclassifier with reference to the capacity of the classifier at any givenspeed, for which reason a consideration of the invention is that theclassifier shall accept the maximum feed in a system and have its ownspeed vary from one relatively short time period to another so as toavoid overloading or clogging, as well as to avoid underloading. Therefore the rake speed of the classifier is controlled or varied withrespect to the significant level of the material against which the rakeswork at the discharge end. The rake speed must be such that the coarsematerial returned to the circuit for regrinding plus the material in thefinished overflow will equal the input feed.

Since the material discharged by the rakes contains liquid, it desirablethat the gauging element be made in the form of a relatively light,airtight drum or rotatable float adapted to ride on the material and tobe partially submerged therein, the degree of submergence beingproportional to the liquid content of the material passing through themachine. This drum or float can be counterbalanced or counterweighted toassist in providing the desired buoyancy. Thus, riding on the material,the float will take a position determined not alone by the compactedheight of the solid particles being discharged, but also by the densityof that material. Accordingly, the performance of the classifier iscontrolled not solely by the actual height of the solids in the materialbut by a combination of that height with the density. This is in harmonywith the practical characteristics of a classifier, because the loadingdepends largely upon the density of the material being handled. In otherwords, if the feed is hard and coarse, it is much drier when dischargedthan is the case when the feed is soft and fine. Consequently, the speedof the classifier rakes is referred to the passage of a materialcomprising massed discrete particles dispersed in a liquid.

In the accompanyin drawings, which illustrates one embodiment ofapparatus by means of which the invention is carried into practice:

Figure 1 represents a side elevation, largely in vertical section and indiagrammatic form, of a Dorr drag classifier, to which the invention isapplied;

Fig. 2, is a fragmentary plan corresponding to Fig. 1; and

Fig. 3, a diagram showing graphically the approximate performance of aDorr classifier without the advantages of the invention, compared withone having the advantages.

Referring to the drawing, the numeral l0, Fig. 1 indicates a dragclassfier of the Dorr type. This type of classifier is provided withrakes. exemplified at l2, which are suspended from a structure I4,mounted for reciprocation so as to provide the peculiar motion necessaryfor the rakes to drag masses of material l5 upwardly on a suitablesurface, such as that indicated at IS. The material operated on by therakes is usually in the form of coarse sands which have settled out fromcrushed ore, these coarse sands being discharged at I 9 over a ledge 20in a cohesive stream, somewhat after the manner indicated. The way inwhich material is fed to the classifier is not important to the presentissue, and, therefore, is not shown. The inclined bottom I5 is part of atank IT.

The classifier is driven from the usual shaft 2|, but, as an importantpart of the invention, the speed of rotation of this shaft isautomatically varied from time to time in accordance with varying needsof operation of the classifier rakes. as hereinbefore stressed.

An advantageous way to impart the desired motion to the shaft 2| is bymeans of an alternating current electric motor of the brush-shiftingtype. In such a motor, if the brushes are shifted, the speed of themotor varies with the position of the brushes on the commutator. Anotherway is to use a direct current electric motor with a rheostat or othersuitable regulating apparatus to vary the speed of the motor. However,all such regulating means are old, and per se do not form a part of theinvention.

In the present instance, it is assumed that a variable speed motor 24 ofthe brush-shifting type is used. Power from the motor 24 to the shaft 2|is transmitted by any suitable and well known means, such as therespective pulleys 25 and 25 with a belt 21 running over these twopulleys. In this instance, a brush shifting mechanism is not shown indetail, since leading manufacturers supply their own particular makes.Here, it is enough to show a shaft 28. the rotation of which in eitherdirection shifts the brushes (not shown) accordingly.

At 29 is a reversible electric motor by means of which the shaft 28 isrotated in either direction in order to control the operation of themotor 24. In the present instance, the speed of the control motor 29 isadvantageously reduced before transmitting its motion to thebrushshifting shaft 28 of the motor 24. Such speed reduction issatisfactorily accomplished by means of a geared speed reducer 30direct-connected to the motor shaft and having a sprocket wheel 3|mounted on the output shaft of the reducer. Another sprocket wheel 32 ismounted on the shaft 28, the two sprocket wheels being operativelyconnected by a chain 34, preferably of the roller type.

In its function of controlling the performance of the drag classifier,the motor 29 is connected electrically with a floating switch arm 35 andwith a motor-operated make-and-break time switch 35. The floating switchincludes an arm 3'! pivoted at 38 and carrying a roller or drum 40 nearits free end, the roller being made, for example, of sheet metal andmounted to rotate at 39.

The switch is so arranged that the sand at the discharge of theclassifier is pushed under the roller 40, thereby raising or lowering itin proportion to the height of the bed 4| of sand being pushed over thedischarge ledge 20 by the rakes. Two movable contacts 42 and 43 aremounted on the arm 35 and are connected to a leg 18 of the electriccircuit, while two cooperating stationary contacts 44 and 45,respectively, are spaced apart sufficiently to give the arm the desiredamount of play between the cooperating contacts, thus limiting theextreme upper and lower positions of the roller relative to theclassifier discharge 4B.

The arm 35 is shown in the neutral position where the switch contacts 42and 43 are approximately midway between the terminals 44 and 45. In thisposition, the roller 40 is running on what may be taken as the mean ornormal classifier load as represented by the quantity of sand dischargedfrom the classifier. If there is an increase over the normal, the rollerrises, finally causing contact 42 to touch terminal 44, thus, undercertain conditions explained later herein, energizing the motor 29 torotate the brush-shifting shaft 28 in the proper direction to cause themotor 24 to speed up, thereby lessening the height of the sand streampassing under the roller. As a result, the contacts 42 and 44 are againseparated and the motor 29 stopped. If there should be a lessening ofthe sand stream below normal and finally to the point where the contact43 touches the terminal 45, the motor 29 again becomes energized, butthis time it will rotate counter to the firstmentioned direction and sowill cause the brushshifting shaft 28 to slow down the motor 24, therebydecreasing the speed of the classifier rakes, with the result that morematerial passes under the roller 40, thus causing the contact 43 to bemoved away from the terminal 45. So long as the normal amount ofmaterial passes under the roller 40, the motor 24 will continue torotate at a given speed.

It is to be observed that the motor-driven, make-and-break time switch36 has the contacts 41 and 48, and is connected in a secondary circuit49, which is itself connected in circuit with the two switch terminals44 and 45. Now, since the reversible motor 29 is also connected in thislatter circuit, it follows that, even though the two floating-switchcontacts 42 and 44 touch,

as hereinbefore stated, the reversible motor 29 will not be energizedunless at the same time the time-switch contacts 41 and 48 are closedalso. The same statement holds true for the two floating-switch contacts43 and 45.

The time switch 36 is adjustable for predetermining the duration of theoperation period as well as the duration of the rest period of thereversible control motor 29, so it becomes possible to obtain almost anydesired relation between the durations of such periods, which means thatthe frequency with which the operation periods occur is alsopredetermined. It is desirable that the operation periods be made asinfrequently as is consistent with the economical operation of both thecontrol equipment and the equipment thereby controlled.

Since the control circuit is periodically closed and opened, or viceversa, it becomes automatically supervisory in character to correctundesired operative conditions occurring in a drag classifier or otherapparatus. The fact that the supervisory function is exercised regularlyprovides the assurance that any particular abnormal condition which maydevelop is allowed to continue not longer than the beginning of the nextcontrol period, and then only long enough to give time for itscorrection.

The roller 49 functions as a buoyant drum float feeler to feel out thesignificant level in the material passing over the discharge ledgethereby gauging the optimum fiow of coarse sands over the dischargeledge in agreement with a given classifier rake speed. Frequently it isdesirable to counter-balance the drum float 40 in order to increase itssensitivity. A counterweight 50 adjustably positioned along an arm isprovided for this purpose, the adjustment being effected by means of aset screw 52, or other suitable means.

The liquid in the classifier is indicated at 53 and the overflow thereofat 54. This overflow carries the finished fine material with it into thedischarge passage 55 from where it is conveyed to any suitable point ofdisposal. The coarse material discharged at [9 plus the fines overflowedat 54 equal substantially the input feed (not indicated) of theclassifier. The input feed may be led into the tank at any usual point.

Reviewing briefly the novel features of the invention, it is to beobserved that the feeler as normally lies at a given level in or on abody of material in transit, and that any material that is added to thenormal body becomes operative to raise or lower, as the case may be, thelevel at which the ieeler rides. The electric contacts are disposed inpositions that are in proximity to the given or normal position of thefeeler, so that when the latter is caused to depart from that position,at least one set of the contacts becomes operative to energize an associated electric control circuit. This energizing of the circuit thenbecomes effective to start an associated reversible motor in the properdirection to bring about a change in the level of the body of materialwhich change tends to correct the undesired condition and to allow theieeler to be restored to substantially its normal position.

The comparison between a Dorr classifier equipped in accordance with thenovel apparatus of the invention and the performance of the sameclassifier equipped only as provided for by Dorr and without the novelapparatus graphically illustrated in Fig. 3, should give a clearcommahension of the differences between those performances.

Referring to Fig. 3, the portion 56 thereof represents by means ofordinates and abscissas, the performance of a Dorr classifier asordinarily adjusted, while the portion 51 represents the per formance ofthe same classifier similarly adjusted but under the control of thenovel apparatus.

For convenience it is assumed in the case of the portion 56, that theclassifier is under observation for a fragmentary period of 28 minutesout of a. regular days run. This period is divided into seven unitintervals of four minutes each, these adding up to the ordinates havingthe arbitrary scaled dimension 58 representing graphically the 28 minuteperiod.

In the case of the portion 51, the dimension of the ordinates resultfrom rectifying the respective areas in the portion 55 and drawn torepresent new conditions presently to be described. The abscissas in theportion 56 have the common dimension 66 and represent an arbitrarilyassumed feed of material composed, for illustration, of a mixture ofcoarse and fine particles. The irregular line 62 represents the divisionbetween the relative prcportions of fine and coarse material passingthrough the classifier at any moment during the different timeintervals, but not segregated as suggested by the diagram. The compositearea above the line 62 represents the fine material, and the compositearea below, the coarse material.

The coarse material load at a particular instant is ascertained bydropping a perpendicular from the line 62 upon the base of the portion56. Accordingly, irregular areas 53 to 69 represent the relativeproportions of coarse material passing through during the respectivefour-minute time intervals, while the corresponding respective spaces IDto 16 above the line 62 represent the corresponding proportions of finematerial. It can readily be seen that the line 52 thus indicates ahaphazard and not an optimum performance in the case of the ordinaryDorr classifier.

The portion 5'! of the diagram visualizes the novel result attained whenthe ordinary Dorr classifier is equipped with the apparatus of theinvention. Here the line 1'! represents the level of separation assumedas the datum for the optimum performance corresponding to certain feedconditions.

Plotting the results of the corrective measures exercised by the novelcontrol apparatus upon the undesirable operative conditions representedin the portion 56, the area 63 is rectified into the rectangular,equivalent area 63-l extending vertically from the base line 18 to thedatum line IT. Similarly, rectifying the irregular areas 64 to 69 intothe respective equivalent rectified areas 64-l to 69-4 will cause theoriginal base ordinate to be changed from the dimension 59 to the newdimension 59, which latter, according to the present assumed conditions,is less than the dimension 58. The changed dimension results because ineach of the areas 63l to 69-l the horizontal dimension becomes larger orsmaller than the horizontal dimensions of the corresponding areas 64 to69 according as the irregular upper boundary of the respective areas 64to 69 is located above or below the broken line I9 the level of whichcorresponds to that of the line H. The irregular areas 10 to 76 areplotted above the rectangles 63l to 69-4, as rectangles 70-1 to l6l,respectively. These latter rectangles represent the corresponding finematerial which overflows from the classifier tank.

The feeler 40 actually feels out the peaks and valleys of the line 62and brings this line up to datum level, thereby producing resultsclosely approximate to optimum performance.

Assuming that the material is moving from right to left along the line19 under the feeler, the latter, above the area 63, immediately speedsup the control mechanism so that the rakes push up coarse material tofill the valley. In the area 64 the feeler acts to level off the peakabove the line 9 by causing the control mechanism to slow down therakes. As the successive irregular areas pass under the feeler, it actsupon the controls to speed up or slow down the rakes as the case may be,so as to even out the peaks and valleys of the line 52. Accordingly, thecorresponding time periods as represented in the portions 56, aredecreased or increased, as the case may be, thereby causing the line 58representing the accumulated time period, to be shortened from thatprevailing in the portion 56 to that represented by the line 59prevailing in the portion 57.

Under the assumed conditions, material having the coarse contentrepresented by the area below the line 52, will in the ordinary Dorrclassifier, occupy a period of 28 minutes to be classified, while in thecase of the invention, acting upon the same material, the time periodfor classifying is reduced according to the ratio existing between thelines 58 and 59. This means giving the classifier a greater capacitywhile actually reducing the wear and tear upon the machinery.

The rectangles 'I JI to T6l represent the fines corresponding to therespective coarse material amounts E3--l to 69--l, these fines asbefore, being overflowed from the classifier tank.

The fact that the device of the invention replaces nothing thatisprovided with classifiers generally. is strongly emphasized.

It is designed to take supervisory control so as to cause the rake speedto vary by minute increments and decrements as required above and belowthe average speed and to follow all ore or other material changes forthe attainment of maximum classification eificiency.

The present ap lication is a continuation-inpart of the one filed by meApril 29, 1942, Ser. No. 441,052, now abandoned.

While the foregoing description of the apparatus is largely specific,the invention is limited only by the terms of the following claims.

What is claimed is:

l. A control system, including in combination, an electric circuit; areversible control motor connected in the said circuit and arranged tocontrol the rate of propulsion of an aqueous pulp through amaterial-handling mechanism; and a floating switch. mechanism havingrotatable float means riding on a portion of a cohesively flowing andfluctuating stream of material handled by said material-handlingmechanism, the said floating switch being connected in the said circuitand arranged so as to have a neutral position which corresponds to agiven state of density of the said aqueous pulp material passing underthe said float means, a second position in which contacts are closed inresponse to a decrease in the density of the said aqueous pulp whereuponthe said float means drops a given distance below the said neutralposition, thereby causing the said reversible motor to be energized androtated in one direction, and a third position in which another set ofcontacts is closed in response to an increase in density of the saidaqueous pulp whereupon the said float means is raised a given distanceabove the said neutral position, thereby causing the said reversiblemotor to be energized and rotated in a direction opposite to the saidone direction.

2. The combination recited in claim 1 wherein there are additionallyprovided means operative to cause the change of rate of propulsion tooccur only Within periodically recurring time intervals.

3. A control system for regulating the operation of a drag classifierwhich has a sand discharge ledge and rakes disposed to drag sands overthe discharge ledge, comprising a rakespeed control mechanism; anormally open electric switch having a rotatable float adapted to rideon the sands being discharged over said discharge ledge and to closesaid switch at predetermined ones of the fluctuating positions of saidfloat; an electric motor having a variablespeed mechanism, the saidmotor being disposed to drive the drag classifier; electrical means forvarying the speed of said electric motor; and electric circuit means inwhich both said electric switch and said electrical speed-varyingmechanism are connected.

A. The combination recited in claim 3 wherein ti electrical means forvarying the speed of the variable-speed electric motor comprises areversible electric motor operable upon the variablespeed mechanism ofsaid variable-speed electric motor.

5. The combination recited in claim 3 wherein there are additionallyprovided means operative to cause the change of rate of propulsion tooccur only within periodically recurring time intervals.

6. A control system, including in combination, an electric float switchhaving a rotatable float element disposed for riding on a cohesivelyflowing and a fluctuating stream of aqueous pulp material whose densityand rate of feed varies from time to time, and having electricmakeand-break contacts at given control levels; means for propellingsaid stream of material; a variable speed electric motor operative onsaid propelling means to control the rate of propulsion of the saidstream of material; electric control means operative to vary the speedof the said motor; and an electric circuit in which the samemake-and-break contacts and the said control means are operativelyconnected.

7. The combination recited in claim 6 wherein the electrical means forvarying the speed of the variable-speed electric motor comprises areversible electric motor operable upon the variablespeed mechanism ofsaid variable-speed electric motor.

8. The combination recited in claim 6 wherein there are additionallyprovided means operative to cause the change of rate of propulsion tooccur only within periodically recurring time intervals.

9. Apparatus operative upon a cohesively flowing stream of materialcomposed of a mixture of fine particles and coarse particles in transit,whose density has a tendency to fluctuate because of variations in thecomposition thereof, the said apparatus including in combination, anelectric float switch having a rotatable and buoyant cylindrical rollerfioat element disposed for riding in or on the said material at a datumlevel, and having electric make-and-break contacts at points in closeproximity to and above and below the datum level; motive means operativeto propel the said material; and variable speed drive means for saidmotive means whereby undue variation in the fluctuating density or thesaid material in transit is corrected; electric control means operativeto vary the speed of the said drive means; and an electric circuit inwhich the said make-and-break contacts and the said electric controlmeans are operatively connected.

10. In an automatic control system where the rate of flow and densitystate of a cohesively flowing stream of pulp-like material constitutesthe control criterion; control means adapted to respond to fiuctuationsin the flow and density of said stream; said control means comprising anoscillating supporting structure; a buoyant cylindrical roller floatrotatably mounted in said supporting structure and adapted to ride in orupon said stream; means efiective to alter the rate of flow of the saidstream; and a power-imparting mechanism operative from the said float tothe rate-altering means.

11. A control system for a drag-type classifier, comprising controlmeans for varying the rake speed of the classifier from moment to momentduring a cycle of continuous running to obtain the optimum operationthereof; and regulating means responsive to variations in the densitystate of the stream of material passing in advance of the dischargeledge of the classifier, for actuating said control means, saidregulating means including a buoyant cylindrical roller float disposedfor riding in or on said stream of material.

12. A control system for a drag-type classifier, comprising controlmeans for automatically increasing or for automatically decreasing therake speed of the classifier during a continuous operation cycle; andmeans responsive to variations in the density state of the stream ofmaterial being discharged over the discharge ledge of the classifier,for actuating said control means, said control means being arranged toincrease the said rake speed to an optimum degree when the said streamof material being propelled through the classifier is relatively deep,and to decrease the said rake speed to an optimum degree when the saidstream of material being propelled through the classifier is relativelyshallow, said responsive means including a buoyant cylindrical rollerfloat disposed for riding in or on said stream of material.

HUGH E. WURZBACH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 997,609 Elmore July 11, 19111,317,956 Carlstedt Oct. 7, 1919 1,603,351 Moyer Oct. 19, 1926 1,619,807Blomfield Mar. 8, 1927 2,001,331 Peale May 14, 1935 2,026,903 MenziesJan. 7, 1936 2,222,030 Hague Nov. 19, 1940 2,299,959 Brentz Oct. 27,1942 2,428,100 Soulen Sept. 30, 1947

